WORLDWIDE PATTERNS OF MITOCHONDRIAL-DNA DIFFERENTIATION IN THE HARBORSEAL (PHOCA-VITULINA)

The harbor seal (Phoca vitulina) has one of the broadest geographic di stributions of any pinniped, stretching from the east Baltic, west acr oss the Atlantic and Pacific Oceans to southern Japan. Although indivi duals may travel several hundred kilometers on annual feeding migratio ns, harbor seals are generally believed to be philopatric, returning t o the same areas each year to breed. Consequently, seals from differen t areas are likely to be genetically differentiated, with levels of ge netic divergence increasing with distance. Differentiation may also be caused by long-standing topographic barriers such as the polar sea ic e. We analyzed samples of 227 harbor seals from 24 Localities and defi ned 34 genotypes based on 435 bp of control region sequence. Phylogene tic analysis and analysis of molecular variance showed that population s in the Atlantic and Pacific Oceans and east and west coast populatio ns of these oceans are significantly differentiated. Within these four regions, populations that are geographically farthest apart generally are the most differentiated and often do not share genotypes or diffe r in genotype frequency. The average corrected sequence divergence bet ween populations in the Atlantic and Pacific Oceans is 3.28% +/- 0.38% and those among populations within each of these oceans are 0.75% +/- 0.69% and 1.19% +/- 0.65%, respectively. Our results suggest that har bor seals are regionally philopatric, on the scale of several hundred kilometers. However, generic discontinuities may exist, even between n eighboring populations such as those on the Scottish and east English coasts or the east and west Baltic. The mitochondrial data are consist ent with an ancient isolation of populations in both oceans, due to th e development of polar sea ice. In the Atlantic and Pacific, populatio ns appear to have been colonized from west to east with the European p opulations showing the most recent common ancestry. We suggest the rec ent ancestry of European seal populations may reflect recolonization f rom Ice Age refugia after the last glaciation.